The objective of this proposal is to trace the development of female sexual behavior in the rat and to determine its origins. Preliminary results show that, under certain condition, female sexual behaviors can be displayed by rat pups as young as 5 to 6 days of age. The proposed research seeks to analyze the reflex components (lordosis and ear wiggling) of such behavior and to determine how and when these components are controlled and modulated by various physiological mechanisms. Specifically, I intend to examine the development of estrogen and progesterone facilitation of female sexual behavior in infant rats, and to examine the ontogeny of sex differences in hormone sensitivity. In addition, the hormonal and behavioral specificity of these precocious behaviors will be described. If time permits, the somatosensory and environmental factors required for the display of sexual behavior in infants will be determined. It is expected that detailed behavioral analysis of the ontogeny of precocious sexual behavior will provide a unique method of analysing the functional development of the neural systems mediating female sexual behavior and the processes underlying sexual differentiation of behavior.